io.grpc.LoadBalancerProvider Maven / Gradle / Ivy
/*
* Copyright 2018 The gRPC Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package io.grpc;
import com.google.common.base.MoreObjects;
import io.grpc.NameResolver.ConfigOrError;
import java.util.Map;
/**
* Provider of {@link LoadBalancer}s. Each provider is bounded to a load-balancing policy name.
*
* Implementations can be automatically discovered by gRPC via Java's SPI mechanism. For
* automatic discovery, the implementation must have a zero-argument constructor and include
* a resource named {@code META-INF/services/io.grpc.LoadBalancerProvider} in their JAR. The
* file's contents should be the implementation's class name. Implementations that need arguments in
* their constructor can be manually registered by {@link LoadBalancerRegistry#register}.
*
*
Implementations should not throw. If they do, it may interrupt class loading. If
* exceptions may reasonably occur for implementation-specific reasons, implementations should
* generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}.
*
* @since 1.17.0
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1771")
public abstract class LoadBalancerProvider extends LoadBalancer.Factory {
/**
* A sentinel value indicating that service config is not supported. This can be used to
* indicate that parsing of the service config is neither right nor wrong, but doesn't have
* any meaning.
*/
private static final ConfigOrError UNKNOWN_CONFIG = ConfigOrError.fromConfig(new UnknownConfig());
/**
* Whether this provider is available for use, taking the current environment into consideration.
* If {@code false}, {@link #newLoadBalancer} is not safe to be called.
*/
public abstract boolean isAvailable();
/**
* A priority, from 0 to 10 that this provider should be used, taking the current environment into
* consideration. 5 should be considered the default, and then tweaked based on environment
* detection. A priority of 0 does not imply that the provider wouldn't work; just that it should
* be last in line.
*/
public abstract int getPriority();
/**
* Returns the load-balancing policy name associated with this provider, which makes it selectable
* via {@link LoadBalancerRegistry#getProvider}. This is called only when the class is loaded. It
* shouldn't change, and there is no point doing so.
*
*
The policy name should consist of only lower case letters letters, underscore and digits,
* and can only start with letters.
*/
public abstract String getPolicyName();
/**
* Parses the config for the Load Balancing policy unpacked from the service config. This will
* return a {@link ConfigOrError} which contains either the successfully parsed config, or the
* {@link Status} representing the failure to parse. Implementations are expected to not throw
* exceptions but return a Status representing the failure. If successful, the load balancing
* policy config should be immutable.
*
* @param rawLoadBalancingPolicyConfig The {@link Map} representation of the load balancing
* policy choice.
* @return a tuple of the fully parsed and validated balancer configuration, else the Status.
* @since 1.20.0
* @see
* A24-lb-policy-config.md
*/
public ConfigOrError parseLoadBalancingPolicyConfig(Map rawLoadBalancingPolicyConfig) {
return UNKNOWN_CONFIG;
}
@Override
public final String toString() {
return MoreObjects.toStringHelper(this)
.add("policy", getPolicyName())
.add("priority", getPriority())
.add("available", isAvailable())
.toString();
}
/**
* Uses identity equality.
*/
@Override
public final boolean equals(Object other) {
return this == other;
}
@Override
public final int hashCode() {
return super.hashCode();
}
private static final class UnknownConfig {
UnknownConfig() {}
@Override
public String toString() {
return "service config is unused";
}
}
}